i have a 85 s10 blazer 4wd 2.8L manual. i recently rebuild the carb and got some help here.

none of the guages in the dash worked when i got it (gas, speed, temp, etc.) so i decided to attempt to fix the speedometer.

after about an hour of trying to remove the speedometer cable, i could not figure out how to remove it out of the firewall, so i just pulled the center wire out and replaced it with the wire from the new one.

now, the speedometer does measure my speed, but it is showing 5mph over the actual speed (measured by gps speedometer). so you would think it would read 5mph when it is stopped but no, it goes below 0 when at stops.
i read another poster that had almost the same thing but his was reading 10mph under the actual. could this be a case of the same situation or something different?

any help would be greatly appreciated.

thanks.

 

Tire size can change the readout on the speedo. Maybe you have the wrong size on the truck? If you look in the drivers doorjamb you will find a sticker that tells you the tire size you should have.

My 93 4x4 takes a 235/75R15 tire.

What size are your rear tires?

 

Sure sounds like there may be incorrect speedo gears in the tail shaft on the transfer case.

To find out how far off it actually is in terms of a percentage, do a few trial runs. Record indicated speed and GPS speed at 15,30,45, & 60. Several runs will give you good numbers to statistically find the true percentage difference. You can then determine what gears you have and swap them out for ones that will give you the proper ratio in the end. Or get a ratio box to convert it.

 

thanks you for the advice and information. i will get more speed readings today on another test run. if i do determine the difference in percentage, will it be possible to find a replacement part for below mentioned speedo gears? i did a quick search on google but didn't find any useful links or products. the only gear like part i saw during the speedo cable replacement was a little lime green plastic part that went into the transfer case before i shoved the end of the cable in. would that be the part i need to replace?

i currently have p215/75/15 tires but there is no stock information to compare it to on the driver's side label because the printed portion is faded and grayed out. from what i could gather online, the stock tires seem to come in 2 different sizes: 205/75R/15's and 235/7R/15's.

thanks again for the help and further advice in advance.

 

Theres your problem... 4x4 comes with 235/75... you have 215/75 means you are 2 sizes smaller than you should have. That will make your speedo read more than you are actually travelling. I think the 205/75 is for 2WD models...

Take one set of 235/75 and call us in the morning, or use the GPS for a speedo.

 

Yeah, that tire difference will cause a +4.1% difference in indicated speed. At an indicated speed of 60MPH, you would really be going 57.5MPH. I would recommend leaving it be until you are in need of a new set of tires and get 235/75R15 tires put on.

 

yupp...i got 35" tires on my toyota and that threw off the speedo big time

and thats compared to stock 27"!

 

thank you guys, that explains my situation completely. i think i'll take swartlkk's suggestion and wait until i need new tires and get the 235's.